1. Field of the Invention
The present invention relates generally to a MOS transistor and a process thereof, and more specifically to a MOS transistor having a metal gate and a process thereof.
2. Description of the Prior Art
Poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as the metal-oxide-semiconductor (MOS). With the trend towards scaling down the size of semiconductor devices, however, conventional poly-silicon gates face problems such as lower performances due to boron penetration and unavoidable depletion effect. This increases the equivalent thickness of the gate dielectric layer, reduces gate capacitance, and weakens a driving force of the devices. Therefore, work function metals that are suitable to be used as high-K gate dielectric layers are used to replace the conventional poly-silicon gates to serve as control electrodes.